This upcoming line of modular interface devices from Machine Collective look useful –

Machinecollective understands your needs and we’re here to help you out! We are working on a range of modules based on frequently used components, sensors and indicators. The prototyping modules are designed to work with development platforms such as Arduino and Wiring. The modules can also be used for other purposes such as circuitbending, DIY synths, analog sequencers or plain old electronics projects.

Developed for use with Arduino, Wiring and other platforms, the hardware is planned for open source release – Machine Collective

The following is just one example there are many others. My gripe with this industry is it’s closed off nature. I can’t just order it and get it I’ve got to get salesman on me which is nasty. Still small companies are easier to take than megacorps.http://www.horner-apg.com/html/products/smartstix/default.asp
Analog and digital I/O, they have a prorietary one and devicenet.

Those are prettier and hopefully cheaper. They don’t state if they speak DMX some industrial protocol or something proprietary. I’d prefer if they were on RS422/485 like DMX or Devicenet.